Plasma treatment of large area substrates such as glass or semiconductor substrates used in the fabrication of flat panel displays or 300 mm silicon wafers respectively pose a series of problems that do not occur in the processing of small area substrates. One problem is simply the generation of plasmas of sufficient area to treat the large area substrate. A second problem is the maintenance of the uniformity of the plasma density and chemistry over such a large area.
The use of inductively or transformer coupled plasma sources (ICP and TCP, respectively) are affected both by the difficulty of maintaining plasma uniformity using inductive coil antenna designs and the cost of fabricating and maintaining such systems which require large and thick quartz windows for coupling the antenna radiation into the processing chamber. The use of such thick quartz windows results in an increase in rf power (and reduction in efficiency) due to heat dissipation within the window.
The use of Electron Cyclotron Resonance (ECR) and Helicon type sources are limited by the difficulty in scaling the resonant magnetic field to large areas when a single antenna or waveguide is used. Furthermore, most ECR sources utilize microwave power which is more expensive and difficult to tune electrically. The use of hot cathode plasma sources results in the contamination of the plasma environment due to the evaporation of cathode material, while cold cathode sources result in contamination due to exposure of the cold cathode to the plasma generated.
The present invention avoids these problems encountered by previous large area plasma processing systems.